1. Field of the Invention
The present invention relates, broadly, to a document reproduction illumination/exposure system and, more specifically to a system for controlling the illumination and exposure parameters of a photographic or microphotographic document reproduction apparatus.
2. Description of the Prior Art
The art recognizes the need to provide both illumination and exposure control, preferably in concert, during various photographic operations. The need to so control exposure times, intensity of exposure radiation and quality thereof, and the like, are quite obvious when it is desired to maximize the quality of photographic reproductions.
Accordingly, the photographic arts have developed various light and exposure metering systems to ascertain the spectral qualities of an object or subject to be reproduced, and which correlate those spectral qualities with like qualities of the image-recording medium. Diverse approaches to accomplish these ends are described in, for example, U.S. Pat. No. 3,760,699, No. 3,855,601, No. 3,872,483, No. 3,992,098, No. 4,015,274 and No. 4,016,574, particularly respecting the control of shutters or other exposure devices in cameras. Conceptually similar devices, albeit, more exotic, are described in U.S. Pat. No. 3,519,347, No. 3,891,317 and No. 4,009,959, exemplary of photographic printers and the like.
In the case of the aforementioned United States. patents which disclose devices for controlling camera shutters or analogous exposure means, the same principally rests upon an operator manipulation of exposure control based upon a numeric or meter display of the spectral qualities of the subject to be reproduced. These displays may involve the matching of movable and stationary needles; a "go-no go" system; a digital display of appropriate exposure characteristics; etc. Moreover, the sensing devices for ascertaining the appropriate spectral characteristics of the subject typically measure gross parameters via one, or possibly two, photodetectors. Consequently, these systems are not adaptable for the broad range of document reproduction requirements.
The same may basically be said of the aforementioned references to photographic printing devices. While well adapted and designed for their intended purposes, the illumination/exposure control systems employed are extremely complicated and intended to control the quality of projecting light from the printer onto the photographic film based upon, primarily, the spectral qualities of the image film and image-receiving film. Consequently, these systems also fail to provide adequate illumination/exposure control when one attempts to adapt the same for the recording of documentary information from an original document of variable spectral qualities onto, for example, a microfiche, microfilm or the like.
Certain devices expressly directed to applications for document reproduction such as, for example, by filming, have indeed attempted to extrapolate from conventional photographic approaches such as those mentioned above. Exemplary of these devices are U.S. Pat. No. 3,947,112 and No. 4,025,190, which rely, essentially, on first establishing a reference datum level corresponding to the optimum exposure and/or illumination settings, and thence adjusting the exposure/illumination parameters in response to a detected indication of, typically, illumination intensity. Conceptually similar is the device disclosed in U.S. Pat. No. 3,640,623, wherein an operator visually compares document or subject density with a density scale, after which evaluation he may automatically establish illumination/exposure parameters. These approaches have obvious drawbacks in requiring substantial operator intervention, and lack of flexibility between various image-recording media without recalibration.
Still further approaches for controlling illumination in a reproduction system are disclosed in U.S. Pat. No. 3,738,242, No. 3,818,496 and No. 3,947,117. The common thread among these references is the maintenance of a prescribed illumination level, wherein illumination is monitored and appropriately adjusted to insure a uniformity thereof. In the first and second mentioned references, the system involved is, for example, a photo-optical drafting machine, or similar apparatus wherein a radiation beam must be precisely controlled in response to relative translation thereof in order to yield a high quality reproduction. In the last mentioned reference, the illuminating radiation is employed for the photocopying of documents or the like, and the system maintains optimum light intensity at the image-forming surface to account for aging of the radiation source. All of the aforementioned approaches are considered either unadaptable, or too esoteric, to be readily adaptable for the control of illumination/exposure parameters in the photographic reproduction of documents; particularly microphotographic reproduction thereof.
Accordingly, the need exists to simply, economically, and yet efficiently provide for the control of illumination and/or exposure parameters in the photographic reproduction of a wide range of original documents having widely differing spectral qualities, and which also provides the ability to employ a wide range of image-recording media likewise having widely differing spectral response characteristics.